Q: Please write about the immune system. What does it mean? How is it damaged? Can one take supplements or injections for it?

A: The immune system is the body’s Army, Navy, Air Force, Marines, Coast Guard and National Guard. It defends us from any foreign intruders — germs, in particular.

One of the largest branches of the immune system is white blood cells. Some white blood cells engage in hand-to-hand combat with germs. Others make antibodies and fire them at invaders like artillery shells.

Some cells in the immune system produce powerful chemicals that engulf and immobilize attackers.

Lymph nodes and the spleen are parts of the immune system. These organs filter body fluids, including blood, and strain from them anything that has made its way into the body.

Without a functioning immune system, people are subject to serious infections.

If the immune system is damaged, it sometimes can be reconstituted. For instance, some viral infections so weaken the immune system that the slightest infection can grow to monumental proportions and kill the infected person. If that person has a deficiency of antibodies, gamma globulin — prepackaged antibodies — can rescue the person from death. If the viral infection is eradicated, the immune system can spring back.

A depletion of white blood cells is another example of a weakened immune system. Antibiotics can kill invading bacteria, and the white blood cell count could return to normal.

Q: My wife is 24. Her recent blood test said she is HBsAg positive. I would like to know something about this, as well as her chances of complete recovery. She has not felt anything unusual, and she believes that she is healthy and fit. She is three months pregnant.

A: “HBsAg” stands for “hepatitis B surface antigen.” The surface antigen is a tiny part of the hepatitis B virus’s outer coat. It indicates infection with that virus.

Your wife needs more tests to see where she stands, as far as the infection goes. Those tests will tell if the infection is active, if her liver is damaged and if she has made antibodies to protect her from the virus.

Most adults recover from hepatitis B. Some, however, develop a chronic infection that can lead to liver cirrhosis and liver cancer. There are treatments for hepatitis B, if treatment is necessary.

You should be checked for infection, and so should the baby upon birth.

(Click here if you are unable to view this photo gallery on your mobile device) The Ruth Bancroft Garden in Walnut Creek celebrates the life of its founder Ruth Bancroft who died at 109 on November 26, 2017. The Ruth Bancroft Garden is a nonprofit public dry garden that was planted by Mrs. Ruth Bancroft in 1972 and was opened to the...